From Wikipedia: On May 31, 1809 on Čegar Hill a few kilometers northeast of Niš, Serbian insurrectionists suffered their greatest defeat in the First Serbian Uprising against the Ottoman Empire (1804-1813). The insurrectionists' advance towards Niš was stopped here and, when the far stronger Turkish forces attacked, the battle was ended by the Serbian commander Stevan Sinđelić, who sacrificially fired at his gunpowder depot in order to avoid surrendering to the Turks, killing himself, the rest of his men, and the advancing Turks.

After the retreat of the Serbian rebel army, the Turkish commander of Niš, Hursid Pasha, ordered that the heads of the killed Serbs were to be mounted on a tower to serve as a warning to whoever opposed the Ottoman Empire

. In all, 952 skulls were included, with the skull of Sinđelić placed at the top. The scalps from the skulls were stuffed with cotton and sent to Constantinople (modern Istanbul) as proof for Sultan Mahmud II.

The tower stood in the open air until the liberation of Niš in 1878. By that time, much of the tower had deteriorated from weather conditions or from the removal of skulls for burial by relatives of killed rebels. In 1892, with donations gathered from all over Serbia, a chapel designed by the Belgrade architect Dimitrije T. Leko was built to enclose what was left of the tower. Today, only 58 skulls remain, including that of Sinđelić.